1. Field of the Invention
The present invention relates to a toner for developing an electrostatic latent image in image forming methods such as electrophotographic methods, electrophotographic recording methods and electrophotographic printing methods.
2. Discussion of the Background
Conventionally, the electrophotographic method is typically a method in which (1) an electrostatic latent image is formed on a photoreceptor formed from a photoconductive material by various means; (2) the electrostatic latent image is developed with a toner to form a toner image; (3) the toner image is optionally transferred onto a transfer sheet such as papers; and (4) the toner image is fixed on the transfer sheet by heating and pressurizing or a solvent vapor deposition to form a copy image.
As a method of fixing the toner image on the transfer sheet upon application of heat, a heating roller fixing method is widely used because of its high energy efficiency. Recently, a system in which a power for the heat source is turned off at a standby time when the fixation is not performed is used for saving energy. In such a system, the heating roller has to be heated and have a desired temperature in quite a short time immediately after the power for the heat source is turned on. Therefore, a fixer used in such a system has to have high heat-energy efficiency and trials are made to make a portion of the fixing roller contacting the toner image supporting face thin. Such trials have enabled the fixing roller to reach the desired temperature in quite a short time.
However, mechanical strength of the roller weakens due to its thinness and a large load cannot be applied thereto. In order to operate such a fixer without problem, a toner has to be fixed at a much lower temperature than that of a conventional toner because heat energy is an essential factor for fixing. Therefore, trials to improve low-temperature fixability of a toner using a resin having a low softening point is typically made. However, when such a resin is used, a fixable temperature becomes lower on the whole and it is difficult to maintain good fixability only by an improvement of a resin.
In order to solve this problem, a wax is conventionally included in a toner to have releasability. In order to sufficiently exert performance of the wax, it is quite important to moderately control dispersed condition thereof on a surface of a toner. When an amount of the wax present on the surface of a toner is large, releasability of the toner due to the wax increases by a heat in fixing. Therefore, the toner has good offset resistance, but at the same time, spent-wax on a carrier and filming over a photoreceptor and a developing sleeve occur to cause a problem in producing a good quality image.
In order to solve these problems, various methods have been suggested, e.g., Japanese Laid-Open Patent Publication No. 8-15907 discloses a method in which fine particles including a part of colorant and a release agent, and a toner composition are mixed in the preliminary mixing process; and Japanese Laid-Open Patent Publications Nos. 9-197715 and 7-287420 disclose a method of pulverizing uniformly with a specific condition in the kneading process. In addition, Japanese Laid-Open Patent Publication No. 5-173354 discloses properties, addition quantity and kinds of a release agent; and Japanese Laid-Open Patent Publication No. 6-161144 discloses dispersed condition of a release agent in a toner.
However, any of these methods does not satisfy both filming and offset resistance.
In addition, recently many copiers have additional printer functions and only one copy or print is often produced. Therefore, a developer agitating time becomes longer for the number of copies and prints. Particularly, in a mode to produce one copy for one original (it is called as 1 to 1 copy and low Duty mode), the developer agitating time per one copy is not less than 4 sec which is 2 to 8 times as long as that of continuous copying while the photoreceptor is rotating at a speed of 150 to 760 mm/sec. In such a mode, a heat stress between the developer and the developer regulating member becomes large, resulting in blocking where the toners mutually melted and solidified; shortening the longevity of the developer; and filming over the photoreceptor.
Because of these reasons, a need exists for a heat resistant toner having a low temperature fixability and stably producing good quality images.
Accordingly, an object of the present invention is to provide a heat resistant toner having a low temperature fixability and stably producing good quality images even in an image forming apparatus where the fixer has a low surface pressure and the developer agitating time is so long as to give much heat stress thereto.
Another object of the present invention is to provide an image forming method using the toner.
Briefly this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a toner including at least; a binder resin, a colorant, a charge controlling agent and a wax (B); in which the charge controlling agent includes at least a compound selected from the group consisting of; an aromatic oxycarboxylic acids, derivatives of thereof, salts thereof and salts of the derivatives thereof; and a zirconium compound (A), and in which the zirconium compound (A) and the wax (B) have a weight ratio (A/B) satisfying the following relationship:
3.0xe2x89xa6(A/B)xc3x97100xe2x89xa660.0
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawing.